By SIMON ROMERO for the NEW YORK TIMES

Noah Friedman-Rudovsky for The New York Times

Animal welfare officials, aware of the risks jaguars pose to visitors, would like Ambue Ari to stop allowing jaguars out for walks.

AMBUE ARI, Bolivia — The mosquitoes descend so ferociously that residents simply call them “the plague.” Piranhas patrol streams. Caiman lurk in ponds. Then there are the monkeys. Visiting volunteers at this jungle outpost have written verses about their propensity to urinate on human belongings.

Across South American hostels, Ambue Ari is legendary.

But the foreigners who make their way to the Ambue Ari animal reserve come here for a very different draw: the big cats. More than two dozen live here in cages, including jaguars, pumas and ocelots. Visitors with training no more extensive than having seen a few episodes of “Mutual of Omaha’s Wild Kingdom” can walk these beasts around the jungle on a leash.

“I’m from Connecticut,” said Ryan Lewis, 31, who came here after serving in the United States Army in Iraq and working as a trader of recycled metals in Toronto. “I was searching for something to do which was really different.”

He certainly appeared to have found that. He spent a recent Sunday morning taking a puma named Tupac on a walk.

Ambue Ari, legendary in hostels up and down South America’s backpacking circuit, has found itself at the center of a controversy among animal welfare officials and big cat experts for allowing visitors such intimate contact with predators that are both dangerous and endangered.

Animal welfare officials, aware of the risks jaguars pose to the visiting volunteers, would like Ambue Ari to stop allowing jaguars out for walks. “We asked them during an inspection to stop this practice,” said David Kopp, an official in the Vice Ministry of Biodiversity in the capital, La Paz.

But in Bolivia, one of South America’s poorest nations, regulatory gray areas can be especially broad here in its remote interior. Mr. Kopp acknowledged that Ambue Ari served an important role in caring for rescued jaguars that overpopulated zoos could not accept. He said the authorities had to remain flexible until new safety measures overseeing the handling of big cats could be put into effect.

Ambue Ari’s directors and many of its visiting volunteers say they are devoted to the animals in their care, some of which are rescued from captivity as abused household pets or illegally trafficked in outdoor markets. By having the big cats walked, Ambue Ari’s directors contend, the animals are given greater freedom than big cats that rarely leave their cages.

“Our cats live with more dignity than those in any zoo,” said Tania Baltazar, 37, the president of Inti Wara Yassi, the nonprofit group that manages Ambue Ari and two other refuges in Bolivia. She said no one at Ambue Ari, which sprawls over 1,991 acres of forest, had been killed by the cats since the refuge was created in 2002.

Still, she acknowledged that some nonfatal injuries were an inevitable result of such close interaction with big cats.

“Scars are nature’s tattoos,” said Ms. Baltazar, showing a few of her own.

The place attracts an eclectic mix. In the depths of January’s rainy season, the visitors numbered 16 souls, including a Canadian carpenter, a Swedish security guard, a British gap-year student and an Australian environmental consultant.

Each pays $10 a day for the privilege of living in a setting somewhere between spartan and squalid. Defiantly off the grid, Ambue Ari has no telephone, no television, no Internet, no air-conditioning, no flush toilets.

The place is a foodie’s nightmare. Breakfast one day consisted of ramen noodles with ketchup. Lunch was white rice, potatoes and a fried egg. Dinner: ditto. For those worried about risks involved with big cats, a veterinarian, Zandro Vargas, is on duty. He applies stitches to people, too.

Jaguars, apex predators that can weigh about 250 pounds, are capable of killing cattle and horses. Attacks on humans are rare but can easily be fatal.

A Bolivia-born jaguar killed a zookeeper at the Denver Zoo in 2007. A jaguar killed a gold miner in Guyana in 2009. In Belize, a jaguar that escaped from its cage at an animal rescue center during a hurricane last October was blamed for the mauling death of an American citizen.

“Relative to their weight, jaguars have the most powerful bite of all cats,” said Rafael Hoogesteijn, a Venezuelan veterinarian who works in Brazil for Panthera, an organization that promotes conservation of large cats. He called the methods used at Ambue Ari “an invitation to disaster.”

Others seemed to agree. “Would I want to wander around the forest with a jaguar on a leash? Well, no!” said Stuart Pimm, an ecologist at Duke University who serves on National Geographic’s big cats initiative, a program to find ways to prevent jaguars and other cats from becoming extinct. “Because there’s no doubt a jaguar can finish you off in a few seconds.”

The thrill of walking a big cat certainly captivates some who make the trek here. Thayer Walker, a writer for Outside magazine who visited Ambue Ari in 2009, described the sensation as being influenced by “the narcotic effects of mainlining 1.5 million years of predatory instinct through a frayed leash cinched at my wrist.”

Robert Thoren, 27, a mountain climber from Los Angeles, arrived here for a brief stay after a bout with pneumonia while backpacking near Lake Titicaca. He ended up staying four years and now oversees construction at Ambue Ari and the group’s two other sites. “It’s no more dangerous to volunteer here than in the Sudan,” he said.

“We’ve had no lost limbs,” added Mr. Thoren, explaining a policy that sequesters cats deemed too dangerous to walk with volunteers in expansive cages, where they can still roam with more ease than in zoos.

The conditions at Ambue Ari seem to instill a sense of communal purpose. Before donning masks of mosquito netting and grasping machetes to cut through the bush, volunteers gather at breakfast for a chant of “Inti Wara Yassi!” — or “Sun, Moon, Stars!” in three Bolivian indigenous languages. Then they venture into the jungle with leashes of rope clipped into carabiners.

Staff members say the rainy season, with its mosquito swarms and moldy clothes, attracts the toughest volunteers. They share fungal medication and Clif Bars, sweating through a climate that feels like a 24-hour sauna. Some battle parasites. Many lose weight, acquiring a waifish heroin-chic look.

“I heard of this place by word of mouth,” said Camilla Nasholm, 22, a Swedish volunteer. “It’s been wonderful so far.”

Some, like Roy Argue, 45, a Canadian volunteer, capture Ambue Ari’s allure in poetry. He posted these lines on his blog: “A monkey peed on all my clothes; ’cause my door someone LEFT OPEN; Stung over and over by fire ants; A scorpion’s crawling inside my pants; What’s the worst that could happen?”

This idyll may not last forever. Poachers have killed peccaries and tapirs within the refuge. The expansion of Bolivia’s agricultural frontier has brought Mennonite settlers to the refuge’s fringes, where they have cut down forest to plant soybeans and sunflowers.

“Where there are mosquitoes there is life,” said Ms. Baltazar, the president of Inti Wara Yassi, explaining why repellent was banned here: because the cats don’t like it and out of respect for the insects themselves. “The creatures in our care come first.”